Abstract
Abstract. We describe Global Atmosphere 4.0 (GA4.0) and Global Land 4.0 (GL4.0): configurations of the Met Office Unified Model and JULES (Joint UK Land Environment Simulator) community land surface model developed for use in global and regional climate research and weather prediction activities. GA4.0 and GL4.0 are based on the previous GA3.0 and GL3.0 configurations, with the inclusion of developments made by the Met Office and its collaborators during its annual development cycle. This paper provides a comprehensive technical and scientific description of GA4.0 and GL4.0 as well as details of how these differ from their predecessors. We also present the results of some initial evaluations of their performance. Overall, performance is comparable with that of GA3.0/GL3.0; the updated configurations include improvements to the science of several parametrisation schemes, however, and will form a baseline for further ongoing development.
Highlights
For more than twenty years, the Met Office has used a single atmospheric model, the Met Office Unified ModelTM (MetUM), for its global and regional Numerical Weather Prediction (NWP) and climate research activities (Cullen, 1993)
A numerical model of the atmosphere requires adiabatic forcing and diabatic processes occurring on scales too fine to be resolved by the dynamical core to be treated by physical parametrisation schemes
Turbulent motions in the atmosphere are not resolved by global atmospheric models, but are important to parametrise in order to give realistic vertical structure in the thermodynamic and wind profiles
Summary
For more than twenty years, the Met Office has used a single atmospheric model, the Met Office Unified ModelTM (MetUM), for its global and regional Numerical Weather Prediction (NWP) and climate research activities (Cullen, 1993). By constraining configurations to perform adequately across a wide variety of systems, scientists can be more confident that model developments seen to improve performance metrics in any one system are doing so by modelling a truer representation of the real atmosphere. It is for this reason that the Met Office is attempting to adopt a single set of atmospheric and land surface model configurations for use in global and regional models across timescales from short-range weather prediction to multicentennial climate projections: the MetUM Global Atmosphere and JULES Global Land.
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